[PDB] Make the pretty dumper output modified types.

Currently if we got something like `const Foo` we'd ignore it and
just rely on printing the unmodified `Foo` later on.  However,
for testing the native reading code we really would like to be able
to see these so that we can verify that the native reader can
actually handle them.  Instead of printing out the full type though,
just print out the header.

llvm-svn: 342295